The present invention relates generally to closed loop control systems, and more specifically to locking mechanisms within closed loop control systems.
Control loop circuits typically use feedback to produce a signal that closely resembles a different signal external to the control loop circuit. Typical control loop circuits can also be made to produce a signal that closely resembles a mathematical function of another signal. For the purposes of this description, the signal produced by the control loop circuit is referred to as the xe2x80x9cproduced signal,xe2x80x9d and the signal that the control loop circuit attempts to replicate is referred to as the xe2x80x9cexternal signal.xe2x80x9d Typical control loop circuits create an error signal that represents the difference between the external signal and the produced signal, and then attempt to minimize the error signal by varying the produced signal. As the external signal varies, the control loop circuit changes the produced signal. The loop is said to be xe2x80x9clockedxe2x80x9d when the error signal is reduced to an acceptable level. Typical control systems maintain a residual error value on the error signal when locked.
In typical control systems, the residual error value can be positive or negative depending on the movement of the external signal. For example, in a control loop that attempts to track the amplitude of the external signal, when the external signal increases in amplitude, the produced signal increases in amplitude in an attempt to follow the amplitude of the external signal. In this case, when the loop is locked, the residual error is negative because the produced signal is less than the external signal. Also for example, when the external signal decreases in amplitude, the residual error present after the loop has locked is positive because the amplitude of the produced signal is greater than the amplitude of the external signal.
The behavior described above creates a situation in which the error signal can vary by an amount equal to twice the maximum residual error. This is because at some lock points, the residual error is a maximum negative value, and at other lock points, the residual error is a maximum positive value. For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a control loop mechanism that exhibits reduced residual error variations.